The present invention relates generally to the field of radiographic imaging equipment and specifically to radiated signal measuring device for determining source to image receptor distance.
The radiographic imager (colloquially known as an x-ray machine) is a well known and widely used diagnostic tool in medical facilities, research laboratories, airport security devices, and other applications. In essence, a radiographic imager comprises a radiation beam source and a radiographic image receptor. The radiation beam source produces a beam of high-energy electromagnetic waves, or x-rays, at a fixed or controllable intensity. Radiation from the radiation beam source passes through a collimator that limits or shapes the radiation beam to the desired area. The high-energy radiation beam passes through a subject, e.g., a human anatomical appendage, and subsequently strikes the radiographic image receptor, which forms an image in response to the relative intensities of the incident radiation. The image receptor may comprise a cassette containing radiographic film, a focal plane array of electro-optic elements, or other suitable receptor.
Due to the technological complexity of the radiographic imaging process, and the potential hazards associated with exposure to the radiation, radiographic imaging equipment is maintained and operated by specially trained radiologic technologists. Prior to initiating radiation exposure to obtain a radiographic image, the technologist monitors and adjusts several critical parameters of the radiographic equipment. In particular, the voltage and current applied to the radiation beam source (and hence its intensity), the duration of exposure, and the Source-to-Image receptor Distance (SID) are critical to obtaining a radiographic image of diagnostic quality.
Since the intensity of radiation incident upon the radiographic imaging receptor changes with SID according to the Inverse Square Law, even slight variations from the optimal SID may have a profound impact on radiographic density, and hence on the quality of the resulting radiographic images. Errors in the measurement of the SID can result in radiographic image being overexposed or underexposed, with resulting distortion or misrepresentation of the anatomy depicted. If the resulting image is not of diagnostic quality, a repeat examination is required, exposing the patient to additional radiation.
Modern medical radiographic imaging equipment includes various actuators and detent switches designed to precisely position the radiation beam source in relation to the image receptor, when the subject can be positioned in a predetermined location and orientation (e.g., on an integral table). However, this positioning and orientation of the subject according to predetermined parameters is not always possible. For example, patients often need x-rays in response to various injuries, which may prevent the patient from assuming a preferred position on the x-ray table. To accommodate such applications, modern medical radiographic imaging equipment includes a variety of pivoting, sliding, and gimbaled mounting apparatuses, which allow for a large degree of variation in the configuration of the radiation source and the radiographic imaging receptor. However, in any configuration other than the predetermined ones, the radiologic technologists may not be able to take advantage of the SID measurement and control capabilities of the radiographic imaging equipment. Additionally, portable units lack such integral SID controls. In such cases, the radiologic technologist must often resort to relatively crude tools, such as traditional tape measure, to ascertain and control the SID. This method is prone to error, and is imprecise even when properly performed. Consequently, the SID of the radiographic equipment may not be properly set for each exposure.
Hence, a need exists in the art for an accurate and reliable method of measuring and indicating the Source to Image Receptor Distance in radiographic equipment.
The present invention relates to a measuring device for determining the distance between two selected points associated with a radiographic imager. The measuring device includes a radiated signal source positioned at a first point and operative to project a radiated signal. The radiated signal is detected by a detector positioned at a second point. A circuit connected to the radiated signal source and the detector determines the travel time of the radiated signal. Based on the spatial relationship between the radiated signal source, the detector, the radiographic imager radiation beam source, and the radiographic image receptor, the source to image receptor distance of the radiographic imager is determined. A display may be connected to the control circuit to output the source to image receptor distance, which display may be periodically or continuously updated. The radiated signal may comprise a laser beam, an ultrasonic signal, a magnetic field, or an RF electromagnetic signal.